1. Field of the Invention
The purpose of the disclosed serial data bus is to allow multiple microprocessors to easily communicate with each other over a common pair of wires using a scheme similar to a telephone party line. The invention relates to data communications links between members of a distributed processing multiplex system in a vehicle such as an automobile. The serial data bus and interface integrated circuit developed and disclosed herein is capable of supporting many types of communication protocols.
2. Description of the Prior Art
Data communications between microprocessors or microcomputers need to communicate with each other in many applications.
Local area networks (LAN) link such microprocessor or microcomputers, allowing one of the microcomputers to seize control of a serial data channel commonly linked to all other microprocessors on the LAN and transmit data to any other unit. The protocols, controllers and software needed in a LAN are very complex, especially in large systems.
An automotive environment is a smaller application and, thus, does not require the complex performance capabilities available in a LAN.
Digital data buses have been designed to handle the above-described data communications link in a small area. Such a system is described in SAE Paper No. 840317, by Ronald L. Mitchell entitled "A Small Area Network For Cars." This document is hereby expressly incorporated by reference. Also descriptive of such a digital data bus is U.S. Pat. No. 4,429,384 to Kaplinsky entitled "Communication System Having An Information Bus And Circuits Therefor."
Also descriptive of developments in this field is SAE Paper No. 860390 by Frederick H. Phail and David J. Arnett entitled "In Vehicle Networking--Serial Communications Requirements And Directions." This document is also hereby expressly incorporated by reference.
The subject invention differs from the art noted above by use of a constant speed, the lack of use of an acknowledgement bit and the lack of a requirements for a tight link between the transmitting station and the receiving stations. Also important in the subject invention is the communication link between the message transmitter and receiver.
Generally, the following U.S. patents discuss collision detection in data communications systems: U.S. Pat. No. 4,281,380 of DeMeas III et al. entitled "Bus Collision Avoidance System For Distributed Network Data Processing Communications System" dated July 28, 1981; U.S. Pat. No. 4,409,592 of V. Bruce Hunt entitled "Multipoint Packet Data Communication System Using Random Access And Collision Detection Techniques" dated Oct. 11, 1983; U.S. Pat. No. 4,434,421 of Baker et al. entitled "Method For Digital Data Transmission With Bit-Echoed Arbitration" dated Feb. 28, 1984; U.S. Pat. No. 4,470,110 of Chiarottino et al. entitled "System For Distributed Priority Arbitration Among Several Processing Units Competing For Access To A Common Data Channel" dated Sept. 4, 1984; and U.S. Pat. No. 4,472,712 of Ault et al. entitled "Multipoint Data Communication System With Local Arbitration" dated Sept. 18, 1984.
The U.S. Pat. No. 4,434,421 patent to Baker et al. deals with a method to reduce the number of collisions. This is done by reducing the number of slave stations attempting bus access until there is one master and one slave station in communication. This differs from the subject invention in that a broadcast method is employed whereby several users can receive the same message.
The U.S. Pat. No. 4,470,110 to Chiarottino et al. discloses a system to exchange messages including an interface. In addition, the '110 patent assigns a priority to an address bit of a particular logical level.
Also of interest is an article in an IEEE publication "Automotive Applications of Microprocessors,"1984; Paper No. CH2072-7/84/0000-0083 entitled "A Data Link For Agricultural And Off Highway Communications" by Boyd Nichols, Vijay Dharia and Kanaparty Rao.
Of paramount importance in the subject invention is the inclusion of the capability to communicate with a serial communication interface (SCI) port, a serial peripheral interface (SPI) port and a buffered serial peripheral interface (BSPI) port.